Plasma cutting tools used to cut or otherwise operate on a workpiece generally comprise a gas nozzle with an electrode therein. Generally, plasma tools direct gas through a nozzle toward a workpiece, with some or all the gas ionized in a plasma arc between the electrode and the workpiece. The arc is used to cut or otherwise operate on the workpiece.
In most tools, a pilot arc is first established between the electrode and the nozzle. Then, the pilot arc is transferred from the nozzle to the workpiece for cutting and/or other operations. For example, some tools use contact-based starting, with the electrode and nozzle initially in electrical contact with one another. While current is passing through the electrode and nozzle, the electrode and nozzle are moved apart to create a gap. A spark across the gap initiates the pilot arc if in a successful starting operation.
Other tools use non-contact starting, which can advantageously avoid wear on the electrode that is aggravated by contact and can avoid the use of moving parts to bring the nozzle and electrode into and out of contact. Various methods and systems have been proposed to initiate the plasma arc by inducing a spark across the gap. For instance, a high frequency, high-voltage signal may be imposed across the gap between the electrode and nozzle. In certain such instances, however, the high-frequency, high-voltage signal may be problematic for at least the reason that RF interference can be introduced. RF interference may cause problems in operation of the tool, such as by feeding back into control systems. Additionally, tools that introduce RF interference must comply with regulations (e.g. FCC and/or IEC regulations) which can increase the cost and complexity of the tool.